Silver halide emulsions and elements containing antifoggants



United States Patent 3,193,386 SILVER HALIDE EMULSHONS AND ELEMENTS CONTAENING ANTKFQGGANTS Clayton F. A. White, Metuchen, N..l'., assignor to E. I. du Pont de Nernours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Nov. 29, 1961, Ser. No. 155,852 7 Claims. '(Cl. %-109) This invention relates to colloid silver halide emulsions and more particularly to colloid silver halide emulsions predominating in silver chloride, for the photographic and lithographic field.

Light-sensitive silver halide emulsion coated elements are used in the graphic arts industry for the production of lithographic and letterpress plates. These elements must be very stable sensitometrically and should be highly resistant to safelight fog. This is because in high quality Work, technicians closely examine the films during development, with the aid of strong safelight illumination, to determine when to terminate development for optimum halftone dot quality. This visual inspection may take place while the film is in the developing solution or when the film is taken out of the developer and held up to the safelight. This places a premium on light-sensitive elements for graphic arts use which have a maximum tolerance for safelight illumination during development.

Photographic emulsions for lithographic purpose are usually composed of silver bromochloride grains predominating in silver chloride which are particularly sus ceptible to safelight fogging when a conventional halftone paraformaldehyde-hydroquinone type developer is used.

It is known, of course, to use 8-hydroxyquinoline or 8- hydroxyquinoline-S-sulfonic acid or its 7-chloro-, 7-bromoand 6-methyl-derivatives as antifoggants either in photographic developers and in certain photographic emulsion layers or contiguous layers. However, the use of S-hydroxyquinoline-S-sulfonic acid compound is completely ineffective in stabilizing the light-sensitive element against orange and red safelights.

It is, therefore, an object of this invention to provide improved photographic silver halide emulsions predominating in silver chloride, and to photographic elements embodying such emulsions for graphic arts purposes. Another object is to provide such emulsions and elements for graphic arts purposes which have improved stability against fog caused by the strong illumination of the conventional darkroom orange and red safelights. Still further objects will be apparent from the following description of the invention.

The improved silver halide emulsions and emulsion layers of this invention are colloid silver halide emulsions predominating in silver chloride and contain a mixture of about 0.15 to about 2.50 grams of unsubstituted 8-hydroxyquinoline and about 0.40 to about 2.40 grams of 8- hydroxyquinoline--sulfonic acid per mol of silver halide. The colloid preferably is gelatin.

Improved lithographic film elements of the invention comprise a colloid silver halide emulsion layer predominating in silver chloride and having in intimate association with the silver halide grains of such layer a mixture of 0.15 to about 2.50 grams of unsubstituted 8-hydroxyquinoline and about 0.40 to about 2.40 grams of S-hydroxyquinoline-5-sultonic acid per mol of silver halide. The mixture of quinoline compounds are preferably in the silver halide emulsion layer but may be present in a water-permeable sublayer or overcoating. When used in contiguous layers, it is preferable to use of the order 3,l3,330 Patented July 6, 1965 ice of from 2 to 4 times the quantities of the two 8-hydroxyquinoline compounds used in the emulsion layer.

The mixture of the two S-hydroxyquinoline compounds is very efiective in preventing safelight fog due to the presence of the unsubstituted 8-hydroxyquinoline compound, and because of the presence of the 5-sulfonic acid derivative is also stabilized against the formation of development fog, especially when metol-hydroquinone developers are used.

The invention is not limited to gelatin silver halide emulsions containing only gelatin as the sole silver halide binding agent since emulsions containing such agents as polyvinyl pyrrolidone, dextrin, dextrans and/or other such agents which increase silver covering power can be present in the gelatin silver halide emulsions. Also, conventional emulsion adjuvants can be present and they are not atfected by the S-hydroxyquinoline compounds.

Thus the invention is equally efiective in both orthochromatically sensitized and non-optically sensitized photographic gelatino-silver halide emulsions. As examples of non-optical sensitizers there may be mentioned sulfur sensitizers containing labile sulfur, e.g., allyl isothiocyanate, allyl diethyl thiourea, phenyl isothiocyanate and sodium thiosulfate; the polyoxyalkylene ethers disclosed in Blake et al. U.S. Patent 2,400,532, and the polyglycols disclosed in Blake et al. U.S. 2,423,549. The amines as disclosed in Staud et al. U.S. 1,925,508 and the metal salts disclosed in Baldsiefen U.S. 2,540,085 and Baldsiefen et al. 2,540,086 may also be used.

Antifoggants which can be used in the emulsions of this invention include benzotriazole and triazaindenes; the emulsions, moreover, may contain the usual hardeners, i.e., chrome alum, formaldehyde, etc. Other emulsion adjuvants well known in the art may be added, e.g., matting agents, plasticizers, toners, optical brightening agents, etc.

The emulsions of the invention may be coated on any suitable support, e.g., cellulose esters, cellulose mixed esters; super-polymers, e.g., polyvinyl chloride (co) vinyl acetate, polyvinyl acetals, e.g., formals, acetals, polystyrene, polyamides, e.g., polyhexamethylene adipamide, and polyesters, e.g., polycarbonates, polyethylene terephthalate, polyethylene terephathalate/isophthalate, esters formed by condensing terephthalic acid and dimethyl terephthalate with propylene glycol, diethylene glycol, tetramethylene glycol or cyelohexane-1,4-dimethanol (he-xahydro-p-xylene alcohol). The vinylidene chloride copolymer coated, oriented, polyester films of Alles et al. U.S. Patent 2,627,088 and Alles U.S. Patent 2,779,684 are especially suitable.

In place of the gelatin binding agents used in the following examples, there can be substituted other natural or synthetic water-permeable organic colloid binding agents. Such agents include water-soluble or permeable polyvinyl alcohol and its derivatives, e.g., partially hydrolyzed polyvinyl acetates, polyvinyl ethers, and acetals containing a large number of intralinear -CH CHOH groups; hydrolyzed interpolymers of vinyl acetate and un saturated addition polymerizable compounds such as maleic anhydride, acrylic and methacrylic acid ethyl esters, and styrene. Suitable colloids of the last mentioned type are disclosed in U.S. Patents 2,276,322; 2,276,323; and 2,397,866. Useful polyvinyl acetals include polyvinyl acetaldehyde acetal, polyvinyl butyraldehyde acetal and polyvinyl sodium o-sulfobenzaldehyde acetal. Other useful colloid binding agents include the poly-N-vinyllactams of Bolton U.S. Patent 2,495,918, the hydrophilic copolymers of N-acrylamido alkyl betaines described in Shacklett U.S. Patent 2,833,650, and hydrophilic cellulose ethers and esters.

EXAMPLE I A lithographic emulsion having a silver halide composition of 30 mole percent silver bromide and 70 mole percent silver chloride and having 20 grams of gelatin present per mole of silver halide for the steps of precipitation and ripening was freed of unwanted, soluble by-.

product salts by washing by coagulation in the manner taught by Waller et al. US. Patent 2,489,341 wherein the silver halide and most of the gelatin were coagulated by commercial sodium lauryl sulfate predominating in sodium dodecyl sulfate, using an acid coagulation environment. Following the washing step, the emulsion coagulum was redispersed in water together with 47 grams of additional gelatin. This redispersed emulsion was treated with a conventional non-optical sensitizer and an optical sensitizer to confer sensitivity, to green light, was digested at 55 C. to'increase sensitivity, was cooled to a temperature of about 38 C. and treated with post-sensitization additives and stabilizers such as additional halides, conventional antifoggants, etc., as is common in the art. Also, there were added to the emulsion, per mol of silver halide, 16.7 ml. of a 10% aqueous solution of a polyoxyethylene compound having the formula:

C SHIT-OT 0112C 2) m- 0 H 74 ml. of an aqueous dispersion of polyethyl acrylate, prepared as described in Procedure A of assignees Nottorf application Ser. No. 94,989 filed Mar. 13, 1961, now US. PatentNo. 3,142,568, and 4 ml. of a by weight aqueous solution of the amphoteric wetting agent, sodium N-coco-beta-amino-propionate and wherein coco refers to a mixture of alkyl radicals corresponding to the fatty acid esters in coconut oil, in which the predominant alkyl radical is dodecyl.

Following the above additions, the resulting emulsion was divided into four equal parts which were treated as follows.

Part 1: No further additions were made and this part served as a control.

'Part 2: To this part there was added 66.7 ml. per mole of 'pose.

anddistilled water containing 2.0 grams of sodium hydroxide. gram, calculated as free sulfonic acid, per mole of silver halide.

Part 3: To this part there was added 33.3 ml. of a solution prepared bydissolving 12.0 grams of 8-hydroxyquinoline in one liter of ethyl alcohol. This provides 0.40 gram of the compound per mol of silver halide.

Part 4: To this portion there were added both 8-hydroxyquinoline-S-sulfonic acid and 8-hydroxyquinoline in the same quantities per mol of silver halide as added in parts two and three respectively.

The four portions of emulsion thus prepared were coated on a photographic film support of the type described in Example IV of Alles US. Patent 2,779,684, on

This provides an equivalent of 0.667

v Water ml which had been coated on both vinylidene chloride coa thin, gelatin-containing, anti-abrasion layer as is common in the art.

Following coating and drying by conventional methods, strips of the resulting films were exposed through a neutral density step wedge in which the density of each step increased by the fourth root of two by a l-B intensity scale sensitometer as described in Mees, The Theory of the Photographic Process, published by Macmillan Company, New York, 1942, page 607 et seq. Two strips coated with each portion of the emulsion, were developed in the following manner.

Procedure A During this development the films were exposed to a Wratten 1-A red safelight illuminated with a 60-wat-t tungsten filament lamp operated at volts which was positioned 30 inches above the developing tray to permit easy inspection of the image during the development. Ordinarily the typical procedure in commercial practice does not comprise developing for any set time but for,

a period sufiicient to providethe quality of halftone image desired in terms of halftone dotsize and density is ascertained by visual inspection. The four minute interval used here is close to, or above, the maximum period of development for lithographic films and for practical purposes, far above the developing time usually used. The procedure here is for the purpose of demonstrating the ability of S-hydroxyquinoline to control fog caused by strong safelight illumination and to show the ineffectiveness of 8-hydroxyquinoline 5-sulfonic acid for this pur- After development, the films were treated in a conventional hardening fixing bath, washed and dried. The sensitometric results were readon a conventional densitometer and the net fog densities are shown in the table below. From this test it was also found that each film possessed excellent speed and contra-st and that the films were essentially the same in these respects Procedure B The second set of strips was exposed and developed in the same manner as in Procedure A using the rocking tray technique but for a period of two and one-half minutes in a high energy continuous tone developer having the following composition:

Methyl-p-aminophenol grams Sodium sulfite (anhydrous) do Hydroquinone d-o Sodium carbonate (anhydrous) do Potassium bromide do Water to make 2.0 liters.

Safelight illumination during this development was of the same spectral transmission as in Procedure A but of a low intensity. The safelight consisted of a l5-watt lamp screened by a Wratten lA filter positioned eight feet from the development tray which is typical of the practice where close visual inspection is not used or required. The practice here is used for copywork and high volume reproduction black and white work where the high quality halftone negatives used for color work, etc. are not required. In this procedure a set, predetermined development time is used. 'Fog resulting from these conditions is of the chemical type resulting from the use of metol-hydroquinone high energy developers. Following development, the films were fixed, Washed and dried as in Procedure A. Net fog density readings resulting from the above processing is shown in the table below along with the results of Procedure A,

Films from Proce Proce- Emulsion Treatment dure A (lure B Portion Control 32 12 8 hydroxyquinoliue-E-sulfonic acid 34 04 8l1ydroxyquin0line 01 13 8-hydroxyquinoline-fisulionic acid 01 03 and S-hydroxtvquinoline.

It will be readily observed that only film sample number four has excellent resistance to both high intensity safelight illumination and chemical fog caused by high energy developers.

EXAMPLE II Example I was repeated and the emulsion was divided into five equal portions and additions of 8 hydroxyquinoline and 8-hydroxyquinoline-5-sulfonic acid were made as shown in the following table.

Additions in Grams of Compound per mole of silver halide Part 1 2 3 4 5 S-hydroxyquinoline 0.15 0.8 1.6 2.4 S-hydroxyquinoline-S-sulionic acid--." 0 1.0 2. 40 0.4 0.4

The emulsions were coated on film base support, dried, overcoated, etc., as described in Example I.

The films were next tested by Procedures A and B of Example I with the following results:

Fog Test, Fog Test, Sample Procedure A. Procedure B Net Fog Net Fog A further advantage of the invention is that the presence of S-hydroxyquinoline also provides a high degree of immunity against many spot-forming, trace contaminants which may be found within the silver halide emulsion or which may come in contact with the surface of the coated film prior to development. The tendency of commercial lithographic films to form intensified spots when in contact with the smoke (or dust) from carbon arc lamps in a typical process camera darkroom is overcome by the novel emulsions and lithographic film elements of this invention.

I claim:

1. A colloid-silver halide emulsion predominating in silver chloride and containing a mixture of about 0.15 to about 2.50 grams of unsubstituted S-hydroxyquinoline and about 0.40 to about 2.40 grams of S-hydroxyquinoline-S- sulfonic acid per mole of silver halide.

2. A gelatino-silver halide emulsion predominating in silver chloride and containing a mixture of about 0.15 to about 2.5 0 grams of unsubstituted S-hydroxyquinoline and about 0.40 to about 2.40 grams of S-hydroxyquinoline-S- sulfonic acid per mole of silver halide.

3. A gelatino-silver bromochloride emulsion predominating in silver chloride and containing a mixture of about 0.15 to about 2.50 grams of unsubstituted S-hydroxyquinoline and about 0.40 to about 2.40 grams of S-hydroxyquinoline-S-sulfonic acid per mole of silver halide.

4. A photographic element comprising a support and a layer of a colloid-silver halide emulsion predominating in silver chloride and containing a mixture of about 0.15 to about 2.50 grams of unsubstituted S-hydroxyquinoline and about 0.40 to about 2.40 grams of B-hydr-oxyquinoline- 5-sulfonic acid per mole of silver halide.

S. A photographic element comprising a film support and a layer of a colloid-silver halide emulsion predominating in silver chloride and containing a mixture of about 0.15 to about 2.50 grams of unsubstituted 8-hydroxyqu noline and about 0.40 to about 2.40 gramsof S-hydroxyquinoline-5-sulfonic acid per mole of silver halide.

6. A photographic element comprising a film support and a layer of a gelatino-silver halide emulsion predominating in silver chloride and containing a mixture of about 0.15 to about 2.50 grams of unsubstituted 8-hydroxyquin-oline and about 0.40 to about 2.40 grams of 8-hydroxyquinol-ine-S-sulfonic acid per mole of silver halide.

7. A photographic element comprising a film support and a layer of a gelatino-silver bromochloride emulsion predominating in silver chloride and containing a mixture of about 0.15 to about 2.50 grams of unsubstituted 8-hydroxyquinoline and about 0.40 to about 2.40 grams of S-hydroxyquinoline-S-sulfonic acid per mole of silver halide.

References Cited by the Examiner UNITED STATES PATENTS 2,691,588 10/54 Henn et a1 96-109 NORMAN G. TORCHIN, Primary Examiner. LOUISE P. QUAST, Examiner. 

1. A COLLOID-SILVER HALIDE EMULSION PREDOMINATING IN SILVER CHLORIDE AND CONTAINING A MIXTURE OF ABOUT 0.15 TO ABOUT 2.50 GRAMS OF UNSUBSTITUTED 8-HYDROXYQUINOLINE AND ABOUT 0.40 TO ABOUT 2.40 GRAMS OF 8-HYDROXYQUINOLINE-5SULFONIC ACID PER MOLE OF SILVER HALIDE. 